Mystery Soreness Solved

Recently I'd been somewhat flummoxed by the fact that Cadence's back seemed to be getting worse again, in spite of the fact that there was nothing work wise that should be making her back sore (in fact her work load was a little lighter than usual), the soreness wasn't indicative of a pull/injury from slipping or something, and she had two saddles that had recently been fitted. So why then was her back sore?  Well, tonight I think I found my answer.
I was doing a light jump/stretch school with the mare tonight, and after our canter work I noticed that my saddle had slipped pretty significantly to the right... impressive considering I'd tightened my girth before cantering to help prevent this. Since I injured (broke and sprained) my foot, my left ankle has been slowly regaining its flexibility as I'm able to do more and more with it. My riding's been evening out again too, but I still am a bit uneven in the jumping saddle as I can't sink my weight down into my left heel as much.  I'd thought it had improved quite a bit, but the slipping saddle suggested otherwise.  And that's when it hit me.  Saddle slipping to the right, more weight in right stirrup, soreness on the right side of Cadence's back.... it's ME that's making her sore!
What a pleasant thing to realize- you're causing your horse pain, and to a certain extent, there's nothing you can do about it.  Even though I do stretches and such for my left foot, I won't be able to ride evenly again unless I keep working on straightening myself out in the saddle.  So to fix the problem I have to keep riding, which in turn will keep adding extra pressure to the right side of Cadence's back.  And while I know that the extra pressure is relatively negligible, and that the situation is largely due to the fact that she's sensitive and expressive, I can't ignore the fact that she's uncomfortable.  She's still in pain, regardless of why or how much.